Heat exchangers (e.g., evaporators and condensers) typically undergo dimensional changes due in large part to thermal expansion/contraction. Because different parts of the heat exchanger may expand and/or contract at different rates, parts of the heat exchanger may be subjected to relatively high mechanical stresses leading to premature failure. This problem is even more pronounced in relatively large heat exchangers used, for example, in commercial refrigeration applications.
Typically, heat exchangers used in refrigeration and air conditioning applications include plural heat transfer fluid carrying tubes and at least two support plates having plural holes through which the respective tubes extend. Such heat exchangers also typically include plural fins for enhancing heat transfer between the fluid in the tubes (e.g., a vapor compression refrigerant) and an external fluid passing through the heat exchanger (e.g., air to be cooled in the case of an evaporator). As the fins expand and contract due to temperature changes, the tubes are pressed against the support plates, which can lead to tube damage and failure. The greater the length of the fins the greater will be the effects of the thermal expansion and contraction.
It is known in the art to relieve mechanical stresses by allowing the tubes to "float". For example, a heat exchanger may be equipped with a fixed support plate and a floating support plate. Thermal expansion and contraction are accommodated by movement of the floating support plate. Another approach involves allowing the tubes to float relative to one of the support plates. However, in both of these approaches, only one end of each tube is able to move, while the other end is relatively fixed.
Still another approach, as shown in U.S. Pat. Nos. 5,020,587, and 5,158,134, is to provide support plates with over-sized holes to allow the tubes to float relative to the support plates. A second set of tubes (which do not carry heat transfer fluid) is rigidly connected to the support plates and the support tubes are connected to the heat transfer fluid carrying tubes by the fins. Although each tube is able to float at both ends thereof relative to the support plates, the additional tubes that are required for support result in increased weight and expense.
There is therefore a need for an improved heat exchanger with flexible tube support to accommodate thermal expansion and contraction of the heat exchanger components.